1. Field of the Invention
The present invention relates to a printing apparatus capable of printing an image using pigment inks and dye inks.
2. Description of the Related Art
Inks used in ink jet printing apparatus are largely classified into two kinds, dye inks and pigment inks. Dye inks are characterized by their production of vivid colors, although they blur easily. Pigment inks do not blur easily and have good water- and light-resistance although they are not good for fine color expression. Considering these characteristics of the inks, a method has been proposed which selectively uses a kind of ink suited to an image to be printed.
For example, as described in U.S. Pat. No. 6,336,705, since characters are printed mostly with a black ink, a pigment ink with a characteristic of not easily blurring is used as a black ink for the printing of characters. Further, since color inks such as cyan, magenta and yellow are often used for printing designs or patterns, dye inks able to produce vivid colors are used for pattern printing. Depending on the image being printed, the black pigment ink and the color dye inks are appropriately switched as described above. This method allows the user of this printing apparatus to produce high-quality printed materials of text documents and patterns without having to become particularly conscious of the kind of ink used.
Further, as described in U.S. Pat. No. 6,951,382, when a pigment ink is left unused for a long period of time, pigment density in the ink may become varied from one location to another. For example, the pigment densities in the upper and lower parts of an ink tank containing the pigment ink may differ, and the use of such an ink tank as is may result in the print density or grayscale level of a printed image differing from that obtained when the pigment is evenly dispersed.
If the ink tank accommodating the pigment ink is left in a static state for a long period, it is necessary to stir the pigment ink thoroughly in the ink tank before the printing operation is resumed. Thorough stirring is effective for producing satisfactory printing results.
If the stirring of the pigment ink is done before the printing operation, the time for ink stirring needs to be added to the time for preparing the printing operation, prolonging the first printout time, the time it takes to start printing a first sheet of print medium.